1. Field of the Invention
The invention generally relates to the field of stimulating tissue growth and healing, and more particularly to apparatus and methods for therapeutically treating damaged tissues, bone fractures, osteopenia, osteoporosis, or other tissue conditions.
2. Description of the Related Art
When damaged, tissues in a human body such as connective tissues, ligaments, bones, etc. all require time to heal. Some tissues, such as a bone fracture in a human body, require relatively longer periods of time to heal. Typically, a fractured bone must be set and then the bone can be stabilized within a cast, splint or similar type of device. This type of treatment allows the natural healing process to begin. However, the healing process for a bone fracture in the human body may take several weeks and may vary depending upon the location of the bone fracture, the age of the patient, the overall general health of the patient, and other factors that are patient-dependent. Depending upon the location of the fracture, the area of the bone fracture or even the patient may have to be immobilized to encourage complete healing of the bone fracture. Immobilization of the patient and/or bone fracture may decrease the number of physical activities the patient is able to perform, which may have other adverse health consequences. Osteopenia, which is a loss of bone mass, can arise from a decrease in muscle activity, which may occur as the result of a bone fracture, bed rest, fracture immobilization, joint reconstruction, arthritis, and the like. However, this effect can be slowed, stopped, and even reversed by reproducing some of the effects of muscle use on the bone. This typically involves some application or simulation of the effects of mechanical stress on the bone.
Promoting bone growth is also important in treating bone fractures, and in the successful implantation of medical prostheses, such as those commonly known as“artificial” hips, knees, vertebral discs, and the like, where it is desired to promote bony ingrowth into the surface of the prosthesis to stabilize and secure it. Numerous different techniques have been developed to reduce the loss of bone mass. For example, it has been proposed to treat bone fractures by application of electrical voltage or current signals (e.g., U.S. Pat. Nos. 4,105,017; 4,266,532; 4,266,533, or 4,315,503). It has also been proposed to apply magnetic fields to stimulate healing of bone fractures (e.g., U.S. Pat. No. 3,890,953). Application of ultrasound to promoting tissue growth has also been disclosed (e.g., U.S. Pat. No. 4,530,360).
While many suggested techniques for applying or simulating mechanical loads on bone to promote growth involve the use of low frequency, high magnitude loads to the bone, this has been found to be unnecessary, and possibly also detrimental to bone maintenance. For instance, high impact loading, which is sometimes suggested to achieve a desired high peak strain, can result in fracture, defeating the purpose of the treatment.
It is also known in the art that low level, high frequency stress can be applied to bone, and that this will result in advantageous promotion of bone growth. One technique for achieving this type of stress is disclosed, e.g., in U.S. Pat. Nos. 5,103,806; 5,191,880; 5,273,028; 5,376,065; 5,997,490; and 6,234,975, the entire contents of each of which are incorporated herein by reference. In this technique, the patient is supported by a platform that can be actuated to oscillate vertically, so that the oscillation of the platform, together with acceleration brought about by the body weight of the patient, provides stress levels in a frequency range sufficient to prevent or reduce bone loss and enhance new bone formation. The peak-to-peak vertical displacement of the platform oscillation may be as little as 2 mm.
However, these systems and associated methods often depend on an arrangement whereby the operator or user must measure the weight of the patient and make adjustments to the frequency of oscillation to achieve the desired therapeutic effect. Thus, there remains a need in the art for an oscillating platform apparatus that automatically measures the weight of the patient and adjusts characteristics of the oscillation force as a function of the measured weight, to therapeutically treat damaged tissues, bone fractures, osteopenia, osteoporosis, or other tissue conditions.